1. Field of the Invention
This invention pertains generally to the field of cockpit indicators or display units that provide flight information to the pilot or flight crew of an aircraft, and more particularly to synthetic vision systems (SVS), enhanced vision systems (EVS), or a combined vision system.
2. Description of the Related Art
Advancements in display technology have provided the ability to depict objects in a three-dimensional synthetic or enhanced scene representative of the scene outside of the aircraft. Although low visibility flight conditions prevent the pilot from visually seeing an object outside of the aircraft, a pilot may see the image or symbol of the object and/or its location in a synthetic or enhanced scene. A pilot who “sees” an object is able to navigate around it.
An aviation regulatory authority or organization possesses the authority of designing and designating instrument approach and departure procedures. In the United States, the Federal Aviation Administration (“FAA”) establishes and provides definitions and ascertainable dimensions of instrument approach and departure procedures. For instance, FAA Order 8260.3B entitled “United States Standard for Terminal Instrument Procedures (TERPS)” dated May 15, 2002 provides criteria used to formulate, review, approve, and publish procedures for instrument approach and departure of aircraft to and from civil and military airports. Also, FAA Order 8260.54A entitled “The United States Standard for Area Navigation (RNAV)” provides criteria for obstacle clearance evaluation of RNAV approach procedures, e.g., Localizer Performance with Vertical Navigation (“LPV”), Lateral Navigation (“LNAV”), Lateral Navigation/Vertical Navigation (“LNAV/VNAV”), and Localizer Performance (“LP”). The criteria in FAA Order 8260.54A support adding an instrument landing system (“ILS”) approach line of minimum to an RNAV (GPS) approach procedure using LPV construction criteria at runways served by an instrument landing system.
In the design of approach and departure procedures, an obstacle clearance surface (“OCS”) may be constructed below a presumed glidepath or climb path of an aircraft to assure the pilot that the path is free from objects. To make such assurance, the OCS is examined for object penetration where such object could include terrain and obstacles. If the OCS is penetrated, then adjustments may be made to address the penetration, where such adjustments include raising the OCS until the OCS is free from object penetration. A consequence of this action, however, may be an unfavorable increase in a minimum altitude to which the pilot may descend the aircraft to a runway in low visibility flight conditions in an approach procedure or affect a pilot's decision to take-off and depart from the airport using a departure procedure.
Although approach and departure procedures are designed to assure that an aircraft route or approach course is free from objects in low visibility conditions, alternative assurance through display technology may be provided by presenting the pilot with an image or symbol of the object and/or its location within a synthetic or enhanced scene of a flight route corridor. Objects within or below a flight route corridor not visible to the pilot that would otherwise penetrate an OCS may now be identified by the pilot and avoided, thereby providing an alternative means for assuring object separation.